1. Field of the Invention
The present invention relates to a distributed timing signal generator as a main component of a tester which is suitable for a high timing accuracy test.
2. Description of the Prior Art
Conventionally, when a timing signal which has a period of no integral multiples of T from the base clock having a period of T is formed, the timing signal formed is provided with a high timing accuracy by using one variable delay circuit in a timing signal generating path as a result of the arithmetic processing of the timing setting data, as shown in Japanese Patent Laid-Open No. 12880/1987. As examples of the related arts, the papers "INDIVIDUAL SIGNAL PATH CALIBRATION FOR MAXIMUM TIMING ACCURACY IN A HIGH PINCOUNT VLSI TEST SYSTEM" (IEEE INTERNATIONAL TEST CONFERENCE 1983, PROCEEDINGS (1983) pp. 188 to 192) and "OPTIMIZING THE TIMING ARCHITECTURE OF A DIGITAL LSI TEST SYSTEM" (IEEE INTERNATIONAL TEST CONFERENCE 1983, PROCEEDINGS (1983) pp. 200 to 209) will be cited.
In the above-described prior art, however, neither the interlocking operations of the timing generators nor the control of the starting times of the timing generators is taken into any consideration, so that in a per-pin architecture tester on which a timing generator per pin is mounted, there is a problem in ensuring the skew between pins with high accuracy. In addition, since counters for generating a period and a delay, respectively, are provided separately from each other, the amount of hardware is inconveniently increased in a per-pin architecture tester.
In the former paper, although a per-pin architecture tester is described, no mention is made of the structure and the mutual control of the timing generators, nor the generation of the timing signals for a driver, for input/output (I/O) control, and for a comparator. In the latter paper, although the generation of the timing signals for a driver and for a comparator is described, since the comparison timing signal for the comparator is delayed in a quantitatively analogous way, the tester is unsuitable for a high timing accuracy test.